The above-mentioned 5-alkoxy-2 (3H) -oxazolone compound can be led to 4-carboalkoxy-2-oxazolidinones which are useful as a synthetic starting material or an intermediate for medicines or agricultural chemicals according to the method described in the following reaction scheme (I): ##STR2## wherein R.sup.1, R.sup.2 and R.sup.3 have the same meanings as defined below, and R.sup.4 represents a C.sub.1 to C.sub.15 alkyl group, an alkenyl group, an alkynyl group or an aryl group which may be substituted.
4-Carboalkoxy-2-oxazolidinones can be easily led to .beta.-hydroxy-.alpha.-amino acid which are useful as medical products, medical intermediate or starting materials thereof by hydrolyzing it with an alkali using an aqueous potassium hydroxide solution according to the method described in, for example, Journal of American Chemical Society, vol. 118, pp. 3584-3590 (1996).
As a conventional method for producing 4-carboalkoxy-2-oxazolidinones, the methods as mentioned below may be mentioned.
1: In Journal of Japan Chemical Society, vol. 82, p. 1075 (1961), phosgene is acted on D,L-threonine in the presence of sodium hydroxide, followed by subjecting to esterification with methanol+hydrochloric acid to obtain 5-methyl-4-carbomethoxy-2-oxazoline.
2 In Journal of Japan Chemical Society, vol. 82, p. 1075 (1961), there is described a method in which N-Cbz-D,L-allothoreonine is subjected to ring opening in the presence of sodium hydroxide, followed by esterification of the resulting compound with methanol+hydrochloric acid to obtain 5-methyl-4-carbomethoxy-2-oxazolidinone.
3: In Journal of Organic Chemistry, vol. 44, p. 3967, (1979), there is disclosed that N-carbobenzyloxyglycine ethyl ester is reacted with benzaldehyde in the presence of lithium diisopropylamide to obtain 5-phenyl-4-carbomethoxy-2-oxazolidinone.
4: In Tetrahedron Letters, vol. 29, p. 2069, (1988), there is disclosed a method of obtaining 3-methyl-5-(1-methyl-3-pentenyl)-4-carbomethoxy-2-oxazolidinone by reacting 3-(1-methyl-3-pentenyl)-2,3-epoxy-1-propanol and methyl isocyanate to obtain 4-hydroxymethyloxazolidine and oxidizing it with a chromium compound, and further esterifying the resulting compound with diazomethane.
However, a preparing process which passes through 5-alkoxy-2 (3H) -oxazolone compound has not yet been known as of today.
An object of the present invention is to provide a novel 5-alkoxy-2(3H)-oxazolone compound which is useful as a synthetic starting material or an intermediate of medicines or agricultural chemicals and a process for preparing the same.